\setMPtext{Text}{TEXT\par UUU}

\startuseMPgraphic{Test}
  fill fullsquare xyscaled(10cm, 5cm) withcolor red;
  label(btex AAA aaa etex, (0, 1cm));
  label(btex BBB \crlf bbb etex, (0, 0cm));
  label(btex CCC \par ccc etex, (0, -1cm));
  label(\MPbetex{Text}, (0, -2cm));
\stopuseMPgraphic

\starttext
  \useMPgraphic{Test}
\stoptext